It means Symantec hasn't tested the Product in their labs with Backup Exec.

If i were you i will check the device with B2DTest tool before using it as a backup target.

http://www.symantec.com/docs/TECH69107

Edit: Here is the confirmation from 2012 HCl

"If the desired device is not already listed in this section, customers are encouraged to download and run the B2D test tool from<http://www.symantec.com/docs/TECH69107> to verify their desired device's level of functionality. Backup Exec Technical Support will be unable to offer assistance if the device experiences failures during the B2Dtest and the customer should contact the hardware vendor for advice and assistance."